Photolari attended a Panasonic press conference and there managers told them this:
The Panasonic GH5 successor will be unveiled within 2021.
They have not unveiled anything about the possible specs. But it’s highly likely that it will have a 30+ MP sensor that can record 8K. Such a sensor already exists and Sony published the specs here:
Still, no guarantee yet this is the sensor that Panasonic is going to use. But hard to believe they will miss the 8K train :)